A vehicle headlamp, for example, an automobile headlight, includes a plurality of lamps arranged therein. JP-A-2015-46235 discloses such a vehicle headlamp.
This vehicle headlamp includes a reflector unit, a substrate on which a Light Emitting Diode (LED) is mounted, and a heat radiation plate. The reflector unit includes a plurality of reflectors with reflective surfaces formed on base members. In each reflector, the base member is integrated by resin molding, and reflective surfaces are formed by aluminum vapor deposition on the respective base members. The substrate is supported by an upper surface of the reflector unit across respective reflectors, and a plurality of LEDs corresponding to the respective reflectors are mounted on the substrate. The upper surface of the reflector unit is formed with holes for guiding light from the LEDs to the reflective surfaces of the reflectors. Further, on a side of the substrate opposite to the surface on which the LEDs are mounted, a metallic heat radiation plate is supported through an insulation sheet across the mounting positions of the LEDs. The heat generated from each LED mounted on the substrate is radiated though the heat radiation plate.
If a relative position between the substrate, on which the LEDs are mounted, and the reflectors is not aligned, it is difficult to obtain the desired light distribution, and if the substrate and the heat radiation plate are separated from each other, there is concern for problems due to heat from the LEDs Therefore, although not explicitly described in JP-A-2015-46235, in general, the reflector unit, the substrate, and the heat radiation plate are fixed to each other by screws. Further, in a typical vehicle headlamp, similar to the vehicle headlamp of JP-A-2015-46235, the reflector unit includes a base member made of resin, and the heat radiation plate is made of metal. Incidentally, in general, the resin and the metal have different thermal expansion coefficients, and the metal has higher rigidity than that of the resin.
In the vehicle headlamp of JP-A-2015-46235, the heat radiation plate is disposed on the reflector unit, in which the reflectors are integrated with each other, via the substrate and the insulating sheet. As described above, the heat radiation plate is disposed across the mounting positions of the respective LEDs, so that the heat radiation plate is disposed across the respective reflectors.
In the meantime, in a vehicle headlamp, the temperature of ambient atmosphere in the vehicle headlamp may increase due to heat generated by a lighting circuit or heat transferred from an engine in addition to heat generated by light-emitting elements such as LEDs. If the thermal conductivity of the reflector unit differs from that of the heat radiation plate and the heat radiation plate has higher rigidity than the reflector unit, when the temperature of the vehicle headlamp rises, stress could be generated on the reflector unit due to the difference in thermal expansion coefficients between the reflector unit and the heat radiation plate.